1. Technical Field
The present invention relates to a display apparatus and a display sheet.
2. Related Art
Electrophoretic displays that utilize the electrophoresis of particles are known to be used for, for example, the image display unit of electronic paper (see, for example, JP-A-2000-127478 (Patent Document 1)). Electrophoretic displays excel in portability and power consumption, and are therefore particularly suitable as the image display unit of electronic paper.
Patent Document 1 discloses an electronic paper that includes a paper and a display layer (electronic ink layer) provided on one surface of the paper. The display layer is realized by a plurality of micro capsules filled with a dispersion liquid of electrophoretic particles, and a binder that holds the micro capsules together.
Patent Document 1 also discloses a printer used to write desired image on the electronic paper. The printer includes a pair of opposing drums. One of the drums has pixel electrodes on the surface. A common electrode is formed on the surface of the other drum. The electronic paper is allowed to pass between the drums with the paper side facing the common electrode, and voltage is applied between the selected one or more of the pixel electrodes and the common electrode as the electronic paper passes through. In response to the applied voltage, the electrophoretic particles in the micro capsules directly below the pixel electrodes migrate, changing the display color in these portions. As a result, desired images such as characters and patterns are displayed on the electronic paper.
However, the electronic paper described in Patent Document 1 is problematic in that the surface of the display layer opposite from the paper side is exposed to outside. As such, the display layer (micro capsules) is susceptible to damage, and when it is damaged, the display characteristics of the electronic paper deteriorate. One way to solve this problem is to protect the display layer by forming, for example, a protective sheet on the surface of the display layer opposite from the paper side.
However, when the protective sheet is conductive, the whole region of the protective sheet is brought to the same electric potential in response to the voltage applied between the selected pixel electrodes and the common electrode as the electronic paper passes between a pair of drums, and as a result the electrophoretic particles migrate in all of the micro capsules of the display layer. In this case, attempts to display desired image on the electronic paper fail regardless of how the pixel electrodes are selected for voltage application based on calculations for displaying desired image.
On the other hand, when the protective sheet has an insulating property, current does not flow in the micro capsules in response to the applied voltage between the pixel electrodes and the common electrode, and desired image cannot be displayed on the electronic paper.
Thus, with the electronic paper of Patent Document 1, desired image cannot be displayed on the electronic paper while protecting the display layer.